The present invention relates generally to the field of non-invasive imaging and more specifically to the field of medical imaging for dynamic, internal tissue, such as cardiac tissue. In particular, the present invention relates to the characterization of internal motion and to the reconstruction of images that account for the characterized motion.
Non-invasive medical imaging broadly encompasses techniques for generating images of the internal structures or regions of a person that are otherwise inaccessible for visual inspection. One of the best known uses of non-invasive imaging is in the medical arts where these techniques are used to generate images of organs and/or bones inside a patient which would otherwise not be visible. One class of medical non-invasive imaging techniques is based on the differential transmission of X-rays through a patient. For example, a simple X-ray imaging technique may involve generating X-rays using an X-ray tube or other X-ray source and directing the X-rays through an imaging volume in which the part of the patient to be imaged is located. As the X-rays pass through the patient, the X-rays are attenuated based on the composition of the tissue they pass through. The attenuated X-rays then impact a detector that converts the X-rays into signals that can be processed to generate an image of the part of the patient through which the X-rays passed based on the attenuation of the X-rays.
Three-dimensional information may be obtained by obtaining additional images at different viewing angles relative to the imaging volume. The angularly displaced images acquired in this manner may then be reconstructed to produce a three-dimensional representation of the imaging volume, including internal structures and organs, that may be displayed on a monitor, printed to a printer, or reproduced on film. A technologist may then review the three-dimensional representation, such as to detect clinically significant irregularities or abnormalities or to assess the three-dimensional landscape prior to an invasive or non-invasive surgical procedure.
Dynamic internal tissues, such as the heart, may present certain challenges for non-invasive imaging techniques, however. For example, in cardiac imaging, the motion of the heart results in inconsistencies in imaging data acquired at different phases of the cardiac cycle. These inconsistencies cause various motion-related image artifacts, such as blurring, streaking, or discontinuities, in the images and/or volumes generated with the imaging data. To reduce the occurrence of motion-related image artifacts, various techniques may be employed to improve the temporal resolution of the imaging system, thereby reducing the effects of the movement of the tissue. For example, temporal resolution may generally be improved by decreasing the time over which the imaging data is acquired. In this way, the amount of motion that occurs within the temporal window associated with the acquisition of the imaging data set is minimized. The temporal resolution may be further improved by choice of reconstruction algorithms and/or techniques. However, these various techniques, alone and in combination, are not currently capable of providing a temporal resolution of approximately 20 ms or less, which is desirable to “freeze” cardiac motion, thereby minimizing motion related artifacts in the reconstructed images. A technique for achieving a temporal resolution consistent with the mechanical and computational constraints present in an imaging system is therefore desirable.